Manufacture of abrasive wheels



April 19, 1949. w. R'. PRATT 2,467,596

MANUFACTURE OF ABRASIVE WHEELS Filed Nov. 8, 1946 M! iapnflfiparyINVENTOR.

Patented Apr. 19, 1949 MANUFACTURE OF ABRASIVE WHEELS Willard R. Pratt,Lcs Angeles, Calif., assigllor to Bevil Company, San Francisco, Calil'.,a copartnership Application November 8, 1946, Serial No. 708,613

6 Claims. 1

This invention has to do with improved methods for the manufacture ofabrasive wheels of the general form embodying a metallic center or corecarrying an abrasive rim. Particularly the invention is concerned withconsiderations having to do with the bonding of the rim to the core, andwhere the rim may be composed of preformer individual segments, with theinter bonding of those segments to form an integrated rim annulus.

At the outset it may be observed that the invention deals with abrasivewheels having sintered rims, by which I mean rim compositions formed forexample of pulverulent metal containing uniformly distributed diamondparticles, integrated by heating to a temperature of incipient fusion orsintering of metallic particles, and at which the composition at alltimes remains essentially solid, though perhaps slightly plastic at themaximum temperature to which it is subjected.

Considering first the problem of. bond formation between the core andthe heated essentially solid rim, my primary concern is to create afusion formed bond while exteriorly confining the rim and expanding thecore into tight or even penetrating engagement with the rim.Difficulties have arisen however because of the fact that upon expansionof the core, the rim material is bodily displaced or expanded againstthe confining medium or mold with such force as not infrequently torupture the mold.

The invention afiords a solution of the dimculty by permitting anexpansion range for both the core and rim within an initial andconsiderable expansion range, and final confinement against furtherexpansion of the rim at a point insuch relation to the temperature risethat the core to rim bond formation will occur while the rim is stronglypressed between the core and mold, but without the latter beingsubjected to breaking pressure. The considerations thus taken intoaccount for the bonding of sintered rims to their cores has given riseto advantages and facilities unattainable by any of the variouspractices heretofore used or proposed for abrasive wheel manufacture.

In accordance with the invention, the core and rim are placed in a mold,the material of which is specially regarded as to its co-eflicient ofexpansion relative to the expansion properties of the core. Preferably Iuse a graphite mold, because of the low coefficient of expansion ofgraphite, of sufficient, but not necessarily of excessive wallthickness, to withstand the highest pressure to be transmitted by therim. The rim 2 material is placed in the mold about the core in suchrelation that the rim material occupies less than the radial distancebetween the mold wall and core. Thus clearance space initially may existbeyond either or both the inner and outer edges of the rim.

Thereafter, as the assembly is heated, the resultant expansion of thecore, or core and rim, is accommodated throughout an initial range intaking up, so to speak, the clearance space or spaces. In the course ofthe expansion, the solid rim is radially displaced or compressed,ultimately to a point of pressing strongly against the circular moldwall because of the pressure transmitting qualities of the sintered rimmaterial. However, since such pressure exertion against the mold occursonly toward the end of the expansion range, such pressure will notassume a rupturing magnitude.

Since dimensional relationships are of significance, it may be preferredto first sinter the rim material before placing it in the mold forbonding to the core, with the advantage that having been compacted andpresintered, the rim will have reached more accurately predeterminableand stable physical and dimensional characteristics.

It is contemplated that the rim may-be composed of preformed segments tobe placed in annular arrangement about the core. The aforementionedadvantages obtain in this instance, with the further effects of the coreexpansion to displace or crowd the segments toward theirinterengagement, and resultant tight pressure of one against the otheras where the segments are themselves to be bonded together. Otherfeatures and objects of the invention are directed to the maintenance orplacement in the 1 interfaces between either or both the core and rim,and between rim segments, of a relatively low melting temperature metalwhich is subjected to compression by the expansion forces of the coreand rim, and which melts to form an alloy bond between the interfacesurfaces.

More complete understanding of the invention will be had from thefollowing detailed description throughout which reference is had'to theaccompanying drawing, in which:

Fig. l is a sectional view showing the core and abrasive rim within atypical form of mold assembly;

Fig. 2 is a cross-section on line 22 of Fig. 1; and

Fig. 3 is a view similar to Fig. 2 illustrating a variational procedurecontemplated by the invention.

It is contemplated that theabrasive rim initially and before bondage tothe core, may be formed as a complete annulus, or as segments to beplaced in the mold in annular arrangement about the core. Fig. 2 showsthe rim II to consist of a preformed annular compact, composed typicallyof finely divided nickel (passing a 325 mesh screen) containing auniform distribution of small diamond particles. The compact ini-'tially will have been formed under high pressure to assume aself-sustaining shape, and desirably may have been heated to sinteringtemperature, resulting in a preformed annulus having, by reason ofitssintered condition, the advantages of more accurate predeterminationof its dimension and other physical characteristics.

. 4 terial, the latter having at its sintering temperature sufilcientplasticity to permit its penetra tion by the core. but without havingthe free mobility of a fiuid.

For purposes of the bond formation between the core and rim. provisionis made for making available at the cote-rim interface a metal The rimII is placed in amold assembly ii about a care if, typically in the formof a circular steel disc whose thickness is less than the rim thickness.The mold assembly comprises a pair of identical mating sections I! andII, the latter of which has a cylindrical bore ll receiving thecorresponding size lower portionila of the section above. The rim II isreceived within opposed annular recesses ll within the end faces of themold sections, while the core if is flatly engaged between the moldsurfaces ll surrounded by the recesses. One mold section may carry anaxial projection ll receivable through opening II in the disc withinbore of the companionsection, to accurately center the core withrelation to mold wall surface ll.

As previously explained, the rim II is pre-I formed'to occupy, whenfirst placed in the mold. a space less than the radial distance betweentherim of the core Iland the mold wall Ii. Thus as shown in Fig. 2, therim may have clearances at either or both fl and 22, respectivelybetween the rim and core, and between the rim and mold wall. The amountof clearancein anygiven instance will depend upon such considerations asthe diameter of the wheel and the expansion characteristics of the core,or the diiferential expansion, upon heating, of the core, and mold.

Using a graphite mold, having relatively low coefiicient of expansion,thetendencyupon heat ing the assembly will be for the steel core toexpand and ultimately close such clearance spaces as will initially haveexisted at either or both the inside and outside of the rim. p

With the rim and core placed in the mold in the condition illustrated byFigs. 1 and 2, the,

mold assembly is placed in a furnace and heated to a temperature whichwill not exceed the sintering temperature of the rim composition,andwill therefore permit the rim to at all times remain an initiallysolid mass. Pressure may or may not be applied to the rimand disc duringthe heating.. Pressure, if desired, may be applied in any suitablemannenas by means of plunger fl bear-' ing against the "upper moldsection. As the heating and temperature rise progress, the core I llexpands, together with some expansion of the rim II, to completely closethe clearance spaces at II and If, this condition preferably. beingreached as the maximum temperature is approached, so that subsequentexpansion will bring the core into. tightly pressed engagement with therim, and the'rim into tightlypressed engagement with the mold surfaceII, but withas into alloy solution. Of course the effectiveness whosemelting temperature is low with relation to the melting point of the rimmatrix metal. in this case typically nickel, so that at the rimaintering temperature, the interface metal will melt and form a bondingalloy solution with the core and rim metals. Bestlresults are obtainedusing the low melting temperature metal in a very thin form, asfor-example by electroplating on the rim surface of the core, or byapplying to either the rim or core surfaces at the interface a thincoating of the metal, or by insertion of a thin foil of the metalbetween the interface surfaces. Excellent bonds have been obtained byinserting within .the interface space a foil of copper, orcopper-containing alloy, the thickness of the foil being not in excessofabout 0.002 inch. Upon heating, the foil melts and goes lntoalloysolution with-the interface metals at a relatively low temperature,within the range of from 150031'Lto 2000 I".. thus enabling the bond tobe formed at such low temperatures and without having to reach therelatively high temperatures required for alloy formation at theinterface in the absence of the low melting temperature metal. Uponexamination of the resulting bond, the copper or copper alloy. will behand to have virtually disappeared by having gone of the bond formationis further increased by the fact that the core expansion will have keptthe foil under tight compression between the core and remain as thecopper melts and alloys with so the interface metals.

out the exertion of such excessive pressure as will rupture the mold.Preferably the parts will be so dimensionally related that at thehighest temperature and point of maximum-expansion, the

Fig. 3 illustrates the adaptation of the invention for bonding to therim a preformed segmental rim. Here therim fl is shown to be composed ofsegments I0 preformed as self-m taining compacts, which as in the caseof the first described rim l0, may initially have been sintered. The egmnts are placed inthe mold about the core 11 with clearances'at 20 or II,or both, respectively at the inside andoutside of the segments. Thearcuate dimensions of the latter may be such that the and surfaces at 30of adiacent segments may initially be inclose proxq imity or ultimatelybrought into pressed interengagement upon expansion of the core and byvirtue of the degree of mobility which the compacts have at sinteringtemperature.

As before, relatively low temperature melting metal, e. g. coper foil,is inserted within the interface at 20, and where bonds are to be formedbetween the segments. themselves, thevpfoil may rim between the core andthe mold wall, are

essentially the same as in the am described instance.

I claim:

core will have slightlypenetrated the l m ma i 1. The method of makinabrasive wheels that includes, placing a metallic core within-and inannularly spaced relation to the wall of a mold, placing between saidcore and wall a relatively high melting temperature rim compact composedof abrasive particles and matrix metal and occupying less than theradial distance between said core and wall, heating the mold. core andrim to a temperature below the melting temperature of the compact and atwhich the compact remains an essentially solid mass to resist expansionof the core, producing b said heating radial expansion of the core intotight engagement with the solid rim and resultant strongly pressedengagement oi the rim against said mold wall, and simultaneously forminga fused bond between said core and rim in the presence of a relativelylow melting temperature metal between said core and rim.

2. The method of making abrasive wheels that includes, placing ametallic core within and in annularly spaced relation to the wall of amold, placing between said core and wall a relatively high meltingtemperature rim compact composed of abrasive particles and matrix metaland comprising a plurality of individual segments occupying less thanthe radial distance between said core and wall, heating the mold, coreand rim to a temperature below the melting temperature of the compactand at which the. compact remains an essentially solid mass to resistexpansion of the core, producing by said heating radial expansion of thecore into tight engagement with the solid rim and resultant stronglypressed engagement of the rim against said mold wall, and

simultaneously bonding said segments together and to said core in thepresence of a relatively low melting temperature metal tightly pressedby -said core expansion between the segments and core and which forms analloy with the core.

3. The method of making abrasive wheels that includes, placing ametallic core within and in annuiarly spaced relation to the wall of amold, placing between said core and wall a rim compact composed ofabrasive particles and matrix metal and occupying less than the radialdistance between said core and wall, maintaining between the core andrim a relatively low melting temperature metal, heating the mold, coreand rim to a temperature below the melting temperature of the compactand at which the compact remains an essentially solid mass to resistexpansion of the core, producing by said heating radial expansion of thecore to tightly press said low melting temperature metal between thecore and rim and to strongly press the rim against said mold wall, andsimultaneously melting said low melting temperature metal to form at theinterface between said core and rim a bond composed of alloy of said lowmelting temperature metal and the core and rim metals.

4. Th method of making abrasive wheels that includes, placing a metalliccore within and in annulary spaced relation to the wall of a mold,placing between said core and walla rim compact composed of abrasiveparticles and matrix metal and occupying less than the radial distancebetween said core and wall, maintaining between the core and rim afoil-like layer of relatively low melting temperature metal, heating themold, core and rim to a temperature below the melting temperature of thecompact and at which the compact remains an essentially solid mass toresist expansion of the core, producing by .said

9 heating radial expansion of thecore to tightly press said low meltingtemperature metal between the core and rim and to strongly press the rimagainst said mold wall, and simultaneously melting said low meltingtemperature metal to form at the interface between said core and rim abond composed of alloy or said low melting teml erature metal and thecore and rim metals.

5. The method oi making abrasive wheels that includes, placing ametallic core within and in annularly spaced relation to the wall of amold, placing between said core and wall a rim compact composed ofabrasive particles and matrix metaLand comprising a plurality ofindividual segments occupying less than the radial distance between saidcore and wall, maintaining between said segments and between thesegments and rim a relatively low melting temperature metal, heating themold, core and rim to a temperature below the melting temperatureof thecompact and at which the compact remains anessentially solid mass toresist expansion of the core, producing radial expansion of the core totightly press said low melting temperature metal between the core andrim and to strongly press the rim against said mold wall, andsimultaneously melting said low melting temperature metal to form at theinterfaces between the segments and between the core and segments bondscomposed of alloy of said low melting temperature metal and the core andrim metals.

6. The method of making abrasive wheels that includes placing a metalliccore within and in annularly spaced relation to the wall of a mold,placing between said core and walla rim compact composed of abrasiveparticles and matrix metal and comprising a plurality of individual S mO pying less than the radial distance between said core and wall,placing between the segments and between the segments and rim relativelylow melting temperature metal foil, heating the mold, core and rim to atemperature belowthe melting temperature of the compact and at which thecompact remains an essentially solid mass to resist expansion of thecore, producing by said heating radial expansion of the core to tightlypress said low melting temperature metal between the core and rim and tostrongly press the rim against said mold wall, and simultaneouslymelting said foil to form at the interfaces between the segments andbetween the core and segments bonds composed of alloy, of said lowmelting temperature metal and the core and rim metals. WILLARD R. PRATT.

REFERENCES CITED The following references are of record in the iiie ofthis patent:

UNITED STATES PATENTS F. T. Van Syckel, The Welding Journal, August,1941, pages 527 and 529.

Tool Tipping Data," The Welding Journal, an 1943, page 61, EngineeringData Sheet No.

